1. Field of the Invention
The present invention relates to a multi-position latching or fastening mechanism for an access lid to a buried pit forming a subsurface chamber for servicing aircraft.
2. Description of the Prior Art
At most modern aircraft terminals the servicing of aircraft on the ground is frequently performed using subsurface pits, which frequently are prefabricated structures. Such aircraft servicing pits are installed at aircraft docking, fueling, and loading areas beneath the surface of the tarmac across which aircraft on the ground travel during docking and departure maneuvers. The pits forming such subsurface chambers are typically constructed of fiberglass, steel, concrete, or aluminum. These pits are typically fabricated as complete enclosures with surrounding walls, sometimes a floor, and an access lid at the top seated within a frame disposed about the neck of the prefabricated pit. When the lid is closed it lies substantially flush with the surface of the surrounding tarmac. Such pits are installed below grade loading and refueling aprons at aircraft terminals, remote parking locations, and aircraft maintenance bases.
The purpose of these aircraft servicing pits is to allow ground support functions to be carried out from subsurface enclosures. These ground support functions include the provision of fuel, the provision of electricity to the aircraft while it is in the docking area, the provision of air for cooling the aircraft interior, the provision of pressurized air for starting the aircraft engines, and for other support activities for aircraft while they are on the ground. The use of subsurface pits eliminates the need for mobile trucks, carts, and other vehicles which are otherwise present in the loading area and which interfere with the arrival and departure of aircraft in the vicinity of a loading gate.
The use of subsurface pits also allows the provision of fuel, power, cooling and pressurized air, and other supplies from a central location. The necessary fluid supplies and electrical power can be generated or stored with a greater efficiency at a central location, as contrasted with mobile generating or supply vehicles.
The pits located below the aircraft terminal area house valves, junction boxes, cooling air terminations, and other terminal equipment that is temporarily connected to an aircraft that has been docked. Umbilical pipes and lines, otherwise housed within the pits, are withdrawn from them through hatches therein and are coupled to a docked aircraft to supply it with fuel, air for cooling the aircraft interior, pressurized air for starting the engines, and electrical power.
The pits are constructed with either hinged or totally removable lids that can be moved between open positions allowing access to the pits and closed positions which are flush with the surrounding surfaces of the docking, loading, or refueling areas across which aircraft travel and beneath which the pits are mounted. To ensure that the pit lids remain nearly level with the surrounding surfaces it is desirable to employ a pit lid latching mechanism. Very typically such a latching mechanism involves a catch depending from the underside of the edge of the pit lid remote from a hinge about which the pit lid is rotatably mounted to its surrounding frame. The catch engages a latch bar secured to an upright interior wall of the pit. The catch is normally moved in rotation about a horizontal axis by means of a lever arm which may be located in a cavity at the underside of the pit lid remote from the axis at which the pit lid is mounted to the frame. Access to this cavity to operate the latch mechanism is normally provided by a gap between the frame and the pit lid adjacent the lever arm. In other types of latching mechanisms different devices are employed to disengage the catch from the latch bar.
One problem that occurs not infrequently with conventional latch mechanisms is that dirt and other runway debris may collect in the seat upon which the pit lid rests. As a consequence, when the pit lid is opened for access to the aircraft servicing equipment or for access to lines located within a subsurface chamber, the debris spreads onto the surface of the pit lid seat upon which the pit lid normally rests. The thickness of this dirt and debris is sometimes sufficient to prevent the pit lid from seating flush against the pit lid seat when the lid is closed again. As a result, the additional thickness of the dirt and runway debris beneath the peripheral edge of the pit lid prevents the catch of the latch mechanism from depending downwardly far enough into the enclosure to engage the latch bar. When this occurs the pit lid will close, but is not latched tightly shut.
Various undesirable conditions can result if an aircraft servicing pit lid is not latched shut. The failure of the catch to engage the latch bar results in a failure to engage watertight seals that are often provided about the periphery of the pit lid. As a consequence, rain and melting snow will wash dirt and debris down into the pit thereby fouling the equipment located within the pit. An even more dangerous situation exists when a jet aircraft passes near a pit with an unlatched lid. The blast from a jet engine can easily blow open a pit lid that is not fully closed and properly latched. When this occurs an aircraft traveling across the surface beneath which the pit is located can damage its landing gear if it rolls across an open pit mouth.